On 2/22/2015 2:28 PM, Alain wrote:
> Le 15-02-19 03:22, scott a écrit :
>>> The density of hydrogen atom in outer space is variable, but the
>>> pressure is in the nano-pascal ( 10^-9 ) range, and we live in
>>> kilohecto-pascal ( 10^5 ), so the influence of the drag is to be
>>> corrected by at least something like a 10^-14 factor.
>>
>> Drag depends on velocity squared, so that would mean if your velocity
>> was 10^7 times higher than on earth, you would experience a similar
>> level of drag.
>>
>> I have no idea what "interstellar velocities are" though, 10^7 or
>> more? :-)
>>
>
> The 10^-9 range is for our spacial neigourhood, or relatively close to a
> star. As you travel farther, it drops conciderably. Between the Sun and
> Proxima Centaury, the vacuum around the moon looks like high pressure.
>
> In space, to have a drag equivalent to 100 Km/h on a road, using the
> 10^14 factor for Earth region, you would need to travel at over 100 000
> 000 000 000 Km/h (10^16 Km/h). That's  /way/ faster than the speed of
> light ! (about 10^9 Km/h)
>
>
>
> Alain


What about within nebulae?

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